Impulse recorder



July 11, 1939.

M. c. BATSEL I IMPULSE RECORDER Filed July 16, 1935 INVENTOR MAX C. TSEL BY 7? v MM ATTORNEY Patented July 11, 1939 PATENT OFFICE IMPULSE RECORDER Max 0. Batsel, Collingswood, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application July 16, 1935, Serial No. 31,589

9 Claims.

This invention relates to the photographic recording of electrical impulses such as those of audio frequency, and has for its principal object the provision of an improved apparatus and method of operation capable of producing a record which covers a relatively wide range of frequencies without substantial distortion and may be reproduced without appreciable ground noise.

Of the various types of photographic sound records now available, the two most generally used are the variable area and the variable density records. These records have not been altogether satisfactory for the reason that the exposure of the photographic record is not at all times proportional to the deflection of the recording galvanometer in the case of the variable area record and of the light valve ribbons in the case'of the variable density record. The resulting distortion of the reproduced sound is due somewhat to the edge effect which may be defined as the spreading of photographic image edges separated from one another by a relatively short distance.

Thus when the volume of sound recorded by 5 the variable area method is relatively low the edges of the sound track closely approach one another, the edge effect operates to make the sound track edges fuzzy or poorly defined and only a limited range of frequencies may be re- 30 produced with an acceptable degree of fidelity. In the case of variable density records, the same undesirable results are encountered when the volume of the recorded sound is relatively high.

Other difficulties encountered in the production of sound records are the distortion of the reproduced sound which results from low light intensity exposure of the emulsion (toe recording), from improper development of the negative or the positive, from improper exposure of the positive or negative during the printing operation and from developing the sound track to the gamma required to produce the desired contrast between the various parts of the picture.

As hereinafter explained, these various difii- 45 culties are minimized or avoided by the utilization of a recording beam which varies in intensity transversely of the light slit from one as parabola.

In toe recording the density of the soundtrack decreases at a rate which increases more rapidly than the decrease in the sound track illumination. In order to correct for this deficiency of 60 the variable density component of the sound track, there may be used a form of light beam which instead of being exactly parabolic in form is somewhat narrowed toward the apex thereby decreasing the sound track transmission due to its reduced width, by the same amount that the transmission tends to be increased by the insuilicient density.

In making sound records according to what is known as the single system where the sound track is recorded on the picture negative, it sometimes becomes necessary to develop the film either more or less than the appropriate development for the sound track in order to secure appropriate development for the picture. If it be necessary to under-develop the negative thereby tending to give reduced contrast, I can compensate for the deficiency by correspondingly increasing the angle between the sides of the parabolic aperture and light beam and correspondingly increasing the curvature at the apex. This will tend to produce an increased variation in the transmission for a given galvanometer deflection or, in other words, will have the same effect as increasing the contrast for a given deflection. Conversely, if the picture negative be under-exposed and is therefore over-developed, too great a contrast of the sound track will result which may be compensated by bringing the sides of the parabola more nearly parallel and using a longer radius at the apex.

Likewise, variations in the printing may be compensated by appropriately altering the contour of the parabolic aperture to correspond with such photographic results as can be predetermined in the same general manner as described above for compensating forvari'ations in' negative development. Where the negative is underexposed and over-developed and the print is similarly under-exposed and over-developed, for example, an S-shaped transmission curve may result. In such case, the two methods of compensation described above may be combined by either using a shorter radius of curvature at the apex and flaring the sides of the parabola toward the wider portion thereof or by conversely making the light beam more nearly semi-circular in form according to the directions of curvature of the transmission curve. The particular shape of beam best suited for any given condition will be readily chosen in view of the foregoing instructions. It will be apparent that, when the aforementioned irregular relations between galvanometer movement or sound impulses and exposure are completely compensated for, therewill be a linear relation between the recorded impulses and the light transmission of the record over the entire range of amplitude;

The invention will be better understood from the following description when considered in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

Referring to the drawing,

Fig. 1 diagrammatically illustrates a sound recorder constructed in accordance with the invention, and

Fig. 2 illustrates the type of sound record produced by the apparatus of Fig. 1.

The recording apparatus of Fig. 1 includes a light source Hi from which light is projected to a galvanometer mirror ll, past a screen I! through the aperture of a screen [3 and through lenses l4 and 15. Light is reflected from the mirror H to the sound track I6 of 'a film record I'I through a lens IS, a light slit in a screen l9 and objective lenses 2!). It will be apparent that the beam of light projected from the source In through the aperture 2| of the screen I3 varies in intensity from the bottom to the top of the aperture. Otherwise expressed, the light intensity of the beam is highest at the base of the aperture and uniformly decreases from the base to the apex of the aperture. The same thing is, of course, true of the aperture image 22 which is projected on the screen [9.

The galvanometer mirror II is vibrated in a well-known manner in accordance with audio current supplied to the conductors 23 on which it is mounted. Under these conditions, theimage 22 of the aperture 2| is vibrated transversely of the light slit 24 in the screen l9 and a record similar to that illustrated in Fig. 2 is produced. It will be observed that this record varies both in area and in density and that the highest density or greatest opacity of the record is found at the narrower sections of the sound record. Thus the record is comparatively transparent at the point 25 where the volume is relatively high and is comparatively opaque at the point 26 where the volume is relatively low. This configuration of the record is due to the fact that the aperture 2|, which is of substantially parabolic form, is illuminated by a light beam which varies in intensity from the base to the apex of the aperture. This effect is produced by the screen l2 which gradually reduces the part of the light source visible through the aperture as the apex of the aperture is approached. As previously explained, the form of the aperture 2| is chosen in accordance with the result to be produced.

I claim:

1. An impulse recorder including means for producing a light beam which varies in intensity from one edge to another along its direction of movement, means for moving said beam in accordance with the impulses to be recorded, and an aperture varying in width restricting said beam to such a shape as to preclude material variation in the relation between the said impulses and the light transmission of the impulse record.

2. An impulse recorder including means for producing a light beam of parabolic contour which varies in intensity from one edge to another, means defining a light slit, and means for moving said beam across said light slit in accordance with the impulses to be recorded.

3. The combination of means for producing a light beam which is substantially parabolic in form and varies in intensity from its base to its apex, means defining a light slit, means for vibrating said beam transversely of said slit, and means for moving a record medium through the part of said beam transmitted through said slit.

4. The combination of means for producing a light beam which is substantially parabolic in form and varies in intensity from its base to its apex, means for defining a light slit, and means for vibrating said beam transversely of said slit whereby a material variation in the relation between said impulses and the transparency of the impulse record is prevented.

5. An impulse recorder including means for producing a light beam which is substantially parabolic in form and is more intense at its base than at its apex, means defining a light slit, and means for vibrating said beam transversely of said slit.

6. An impulse recorder including means for producing a light beam which varies in intensity from one edge to another along its direction of movement, means for moving said beam in accordance with the impulses to be recorded, and an aperture varying in width restricting said beam to such a shape as to cause the light transmission of the impulse record to have a linear relation to the impulses recorded.

7. An impulse recorder including means for producing a light beam which varies in intensity from one edge to another along its direction of movement, means for moving said beam in accordance with the impulses to be recorded, and an aperture varying in width restricting said beam to such a shape as to cause the total light transmission of the impulse record to have a linear relation to the impulses recorded.

8. In combination a light source, means directing light from said source to a galvanometer adapted to be vibrated in accordance with impulses to be recorded, a penumbra mask between said light source and said galvanometer, a slit plate having a narrow slit therein, means for directing light from said galvanometer to said slit plate whereby the beam of light is vibrated across said plate in accordance with the impulses to be recorded, means for focusing light passing through said slit upon a film, and an aperture plate in the path of said light between said source and the last-named means, said aperture plate having an aperture therein varying in width longitudinally of said slit in such a shape as to compensate for variations in light transmission of the impulse record which might otherwise occur for producing a record having a substantially linear relation between its light transmission and the recorded impulses.

9. In combination a light source, means directing light from said source to a galvanometer adapted to be vibrated in accordance with impulses to be recorded, a penumbra mask between said light source and said galvanometer, a slit plate having a narrow slit therein, means for directing light from said galvanometer to said slit plate whereby the beam of light is vibrated across said plate in accordance with the impulses to be recorded, means for focusing light passing through said slit upon a film, and an aperture plate in the path of said light between said source and the last-named means, said aperture plate having an aperture therein varying in width longitudinally of said slit in such a shape as to compensate for variations in light transmission of the impulse record which might otherwise occur for producing a record having a substantially linear relation between its light transmission and the galvanometer deflection.

MAX C. BA'ISEL. 

